1. Field Of the Invention
The present invention is directed to a method for detecting tachyarrhythmia of the heart, as well as to an apparatus for treating tachyarrhythmia with means for detecting tachyarrhythmia operating according to the method and having an output connected to means for triggering the tachyarrhythmia treatment.
2. Description of the Prior Art
Tachyarrhythmia are disturbances in the rhythm of the heart exhibiting an unnaturally elevated frequency, caused by pathologies of the stimulus formation or stimulus conduction in the heart. Such tachyarrhythmia lead to a reduced chamber filling and ejection power of the heart and, in the worst case, can lead to a standstill of the blood conveying through the heart given the presence of ventricular fibrillation.
European Patent 0 108 360 discloses that a rapid heart rhythm, when caused by retrograde transfer, can be terminated by electrical stimulation pulses from a heart pacemaker that are delivered to the heart at specific times with reference to the tachycardia heartbeats.
U.S. Pat. No. 4,403,614 discloses an implantable cardioverter, wherein the heart frequency is calculated by measuring the spacing of successive R-waves of the heart. Rhythm disturbances having frequencies of less than 140 beats per minute are thereby classified benign and rhythm disturbances having frequencies between 140 and 300 beats per minute are thereby classified pathological because they develop into ventricular fibrillation, whereas a ventricular fibrillation is assumed to be present if frequencies of more than 300 beats per minute are detected. When a tachyarrhythmia classified as pathological is detected, a cardioversion of the heart is triggered with a cardioversion energy that lies between the standard stimulation energy of heart pacemaker pulses and the energy required for defibrillation purposes. A defibrillation of the heart occurs given the detection of ventricular fibrillation.
The different therapy methods of anti-tachycardia stimulation, cardioversion and fibrillation require a recognition of the rhythm disturbances of the heart. The detection of tachyarrhythmia using only a heartbeat detector and evaluation of heartbeat-frequency-related criteria such as frequency, sudden frequency rise and persistent, high-frequency values can be problematical. In particular, there is the risk that a rapid sinus rhythm will be misinterpreted as tachycardia.
U.S. Pat. No. 3,942,536 discloses an implantable cardioverter, wherein the pressure in the right ventricle is acquired with a pressure sensor at the end of a catheter; as soon as the measured pressure drops below a limit value over a prescribed chronological duration, a cardioversion of the heart is triggered. Heretofore, however, the production of pressure sensors that are adequate for this purpose has not succeeded, in part because of the difficulty of devising a pressure sensor which is insensitive enough so that the measured results thereof are not falsified by the deposits of fibrous tissue, but which has sufficient sensitivity so that static pressures can also be precisely measured.
It is proposed in U.S. Pat. No. 3,805,795 to utilize, for example, the heartbeat frequency acquired with a heartbeat detector as a first criterion and to utilize the mechanical heart activity acquired with a motion sensor in the heart as a second criterion for the detection of tachyarrhythmia, and to trigger a shock treatment of the heart when both criteria are simultaneously met over a prescribed chronological duration.
U.S. Pat. No. 5,085,213 discloses an implantable defibrillator/cardioverter, wherein pressures measured in the heart and frequency criteria are utilized for identifying disturbances in heart rhythm. As in the aforementioned U.S. Pat. No. 3,942,536, suitable pressure sensors having adequate long-term stability have hitherto not been available, particularly for the measurement of static pressures.